A novel telephone station signaling lock circuit was disclosed in the previously referenced U.S. patent entitled "Telephone Station Signaling Lock Circuit". As disclosed in that patent application the signaling circuit was locked or disabled by a microprocessor in response to operation of a station lock pushbutton. To unlock or enable the signaling circuit, the station lock pushbutton was again operated and selected keypad pushbuttons were subsequently operated. If the character signals provided by operation of these keypad pushbuttons are identical to a predetermined unlock code, the microprocessor then unlocks or enables the signaling circuit. However, if the unlock code is not known, the signaling circuit of a locked telephone station can not be unlocked, even in cases of emergency. The Master Unlock Circuit of the present invention overcomes this limitation.